The invention relates to a switch assembly for use in magnetic levitation railways.
A switch assembly of the type of interest here comprises a so-called flexible switch (such as “Magnetbahn Transrapid—Die neue Dimension des Reisens” [“Transrapid Maglev—The New Dimension in Travel”], Hestra-Verlag Darmstadt 1989, pp. 32-35, DE 10 2004 015 495 A1). The essential component of such a flexible switch is a flexible steel girder that is 50 m long, for instance, or even longer and that bears the load of the travel way and equipment parts thereof. The girder is located in stationary fashion on one end and otherwise, by means of a plurality of load-bearing frames and carrying wheels mounted on them is supported movably on rails that are located transversely to its longitudinal direction, which is also the travel direction. For adjusting the switch, the load-bearing frames can be moved back and forth along the rails, as a result of which the girder is flexed and is aligned selectively with one of a plurality of travel ways that branch off from the switch.
For displacing the load-bearing frames, drive mechanisms have first been used, whose piston rods were pivotably connected to the load-bearing frames and whose cylinders were pivotably connected to stationary bearing blocks. However, since sealing problems and space problems inevitably arise when cylinder/piston assemblies are used, a switch assembly of the generic type described at the outset has already been disclosed as well. It has a rack, extending transversely to the travel direction, which meshes with a gear wheel that can be set to rotating, by means of a drive shaft located parallel to the longitudinal direction of the girder and driven by an electric motor mounted on the load-bearing frame. When the motor is on, the gear wheel rolls along the rack and in the process carries the entire drive mechanism, the associated load-bearing frame, and an associated girder portion along with it.
Because of the comparatively great length of the girder, in the construction of the switch assembly its possible change in length from temperature fluctuations must be taken into account as well. This purpose is served, in the switch assembly of the type defined at the outset, by dry slide bearings, by means of which the girder is braced on the load-bearing frames, and which make the requisite axial and rotary motions possible between the girder and associated parts of the load-bearing frames. The carrying wheels, guided movably on the rails and provided with wheel flanges on both sides, prevent motion of the load-bearing frames parallel to the travel direction, while the slide bearings allow expansion or contraction of the girder relative to the load-bearing frames in that direction. So that the motor when on will not rotate about the drive shaft, it is braced on the girder by means of at least one support element, and between the motor and the girder, there is a further dry slide bearing, which enables motions of the girder relative to the motor.
Because of the construction as described, the slide bearings that brace the girder have a plurality of functions. They must not only bear the weight of the girder but also enable relative motions between the girder and the load-bearing frames. As a result, comparatively long, stable slide bearings have to be provided, and therefore the entire apparatus comprising the girder and the load-bearing frames is relatively complicated and expensive. Since furthermore the girder may be comparatively large in all three dimensions, comparatively high strains can occur in the girder upon temperature fluctuations and especially an uneven amount of sunshine, and these stresses distribute the loads correspondingly unevenly to the slide bearings. This can lead to very high local loads on the slide bearings and in extreme cases to blockage of the slide bearings and furthermore to major noise production in the slide bearings. Under some circumstances this can shorten the service life of the slide bearings considerably.